JP6008963B2 - Method of drinking water - Google Patents

Description

  The present invention relates to a method of making water a drinking water, in particular a method comprising the step of coagulation-soft flocculation using a liquid composition of specially solubilized cationic starch together with a metal salt.

  In the water field, treatment methods are very diverse. For example, prior to release into the environment, wastewater or industrial process water is not treated in exactly the same way, depending on the nature of the water.

  For drinking water, it is necessary to obtain high purity water at the end of the process. Water allocation is an important issue for the population and has been increasingly regulated over the years. Highly pure drinking water is obtained using a very specific method that is quite different from other water treatment methods, where the resulting water may be of lower purity.

  To obtain drinking water, the aqueous solution can be pumped from ground water or from surface water that requires treatment, such as water from a lake or stream. This aqueous solution always comprises an indefinite amount of suspended particles, which must be removed.

  For example, coarse particles generally larger than 1 mm can be removed in a preliminary stage by passing an aqueous solution through a screen. This stage is also referred to as a “screening process”.

  Finer suspended particles can also be removed by separation from the aqueous solution to be treated, for example by gradient method or flotation.

  The gradient method consists of placing the solution in a settling tank, also called a “settling separation tank”, so that the suspended particles sink to the bottom of the tank. Purified water is thus recovered by the gradient method.

  The principle of flotation is to mix the aqueous solution with air in the flotation device to collect particles at the surface. The water thus treated is collected at the bottom of the flotation device.

  However, aqueous solutions generally comprise fine particles that are difficult to separate, especially very small colloidal particles generally in the range of 1 nm to 1 μm, which are particularly difficult to separate.

  For easier and faster separation of these fine particles, a coagulation-soft aggregation process is first performed. This step consists of agglomeration of suspended particles. These coarser agglomerated particles are then separated more easily and more quickly by the process described above.

  To perform coagulation-soft aggregation, coagulants and coagulants are used alone or in admixture. These agents may be selected from ferric or aluminum salts, anionic or cationic polyacrylamide, and nonionic, anionic or cationic starch.

  In general, the coagulant and flocculant are mixed in two separate stages with the aqueous solution to be treated in a tank referred to in this application as a coagulation-soft flocculant tank. This tank is composed of a first tank generally referred to as a “coagulation tank” and a second tank referred to as a “soft coagulation tank”, in which a coagulant and a coagulant are respectively charged. These solidification phenomena are generally explained by destabilization of the particles, especially colloids, and soft agglomeration due to agglomeration of the particles thus destabilized. Next, a separation step is applied to an aqueous solution comprising agglomerates of particles or colloids called floc. Purified water and sludge consisting of agglomerated floc is thus recovered.

  In order to measure the effectiveness of this coagulation-soft aggregation process, the chemical oxygen demand (COD) of purified water, which is an indirect measurement of the concentration of organic or inorganic substances dissolved or suspended in the water, is measured. It is possible. The amount of oxygen required for complete chemical oxidation of these materials is measured. The amount of organic carbon dissolved in the treated water can also be measured.

  As an alternative, it is also possible to measure the turbidity level or turbidity of the aqueous solution before and after this coagulation-soft flocculation step.

  This turbidity is measured by a nephelometer (also called a turbidimeter), which is measured in nephelometric turbidity units (NTU).

  In this way the decrease in turbidity is measured and can be expressed as a percentage.

  Another method also measures the absorbance of the treated aqueous solution at a given wavelength.

  In order to further make the water suitable for drinking, the purified water thus consists of passing the water through one or more filters in order to remove certain residual contaminants. Is generally applied. It is also possible to carry out a disinfection step consisting of adding an agent or using a treatment that can eradicate the bacteria present in the water. These last-mentioned treatments are particularly useful in the method of drinking water.

  The water treatment method is generally a continuous process.

  When a filtration step is performed to make the water suitable for drinking, the last particles remaining in suspension are removed from the aqueous solution by passing through a filter. Therefore, during this filtration, particles accumulate inside the filter and the filter becomes clogged. This results in a “head loss”, ie a reduction in the filtered water flow at a constant pressure subjected to filtration. In order to avoid having to stop the process too frequently to replace a clogged filter so that there is no need to increase the pressure to keep the flow rate constant, the aqueous solution in which this filtration step is performed is generally It must have a low turbidity of less than 1.5 NTU, preferably less than 1 NTU.

  Similarly, in order to carry out the disinfection process, it is advantageous to have as clear water as possible in order to facilitate this disinfection process (reducing the amount of active substance required to reduce the strength of the disinfection process) ).

  In addition, national regulations generally provide low turbidity for drinking water distribution. In France, for example, this turbidity must be less than 1 NTU.

  Therefore, the decrease in turbidity obtained during the coagulation-soft aggregation process is very important in the method of drinking water.

  Drinking water treatment methods using cationic starch-based agents have already been described. In effect, these cationic starches have the advantage that they are made from renewable plant resources and are available in large quantities.

  One example of a method for drinking water is US Pat. No. 5,543,056, which describes a method in which a coagulant, which can be cationic starch, and a flocculant, which is clay, are added to an aqueous solution. It is done. This patent also describes a comparative test, a method of drinking water using a metal salt as a coagulant in the first step, and a flocculant selected from chitosan or polyacrylamide in the second step.

  It is also known to simultaneously use enzymatic or chemically liquefied cationic starch in combination with additional coagulants in the treatment of wastewater released into the environment or recycled to the factory. . To treat very low viscosity aqueous solutions, it is known to use cationic starches that are also low viscosity so that they can work effectively with additional coagulants.

  As a document describing a method using such a starch, International Publication No. 20000019403A1 pamphlet can be cited. This describes the treatment of industrial process water, the use of cationic starch in combination with cationic polyacrylamide type flocculants. The effectiveness of the coagulation-soft flocculation process, particularly using a mixture of cationic polyacrylamide and cationic starch, is investigated in Example 10. The tests in the examples show that liquefied and thus low viscosity cationic starch combined with cationic polyacrylamide exhibits greater efficacy than non-liquefied cationic starch.

US Pat. No. 5,543,056 International Publication No. 20000019403A1 Pamphlet

  At present, there is still a need for new methods for drinking water.

  In particular, it would be advantageous if this method could be carried out with very short processing times, using small amounts of chemicals and without changing the equipment used in conventional methods for these treatments. It is. It should give a considerable reduction in the turbidity of the treated water.

  This has been achieved by the applicant by conducting research on methods of drinking water.

  In effect, Applicants have found that when a cationic starch liquid composition is used in a coagulation-soft flocculation process with a ferric salt and / or an aluminum salt, the cationic starch traditionally used in this field In comparison, it has been found that it has properties that make it possible to bring about a considerable reduction in the turbidity of the aqueous solution to be treated in particular. When charged to the water being treated, this particular starch must be in a form that can be dissolved in the liquid composition. This composition can be used with a metal salt in any type of method for obtaining drinking water comprising a coagulation-soft aggregation process.

In particular, the present invention
a) adding a liquid composition comprising solubilized cationic starch to the aqueous solution to be treated;
b) adding one or more metal salts selected from ferric salts and aluminum salts to the treated aqueous solution;
c) stirring the aqueous solution containing these additives;
d) separating the solidified solids by sedimentation or flotation;
e) recovering purified water, comprising a coagulation-soft flocculation step, comprising a step of drinking water from an aqueous solution having a suspended solid,
Said steps a) and b) are carried out in any order, they can be carried out separately, simultaneously or by means of a liquid composition comprising both said solubilized cationic starch and said metal salt, Steps a) and b) are followed by said steps c), d), e),
The liquid composition comprising the cationic starch has a viscosity measured according to test A of greater than 1000 mPa · s, which adjusts the dry matter of the liquid composition to 10% and then results in Measuring the Brookfield viscosity of the resulting composition at 25 ° C.

Shows a gradual change in turbidity as a function of starch weight compared to the total amount of starch and metal salts.

  Test A used to measure the viscosity of the liquid composition is applicable regardless of the form of the liquid composition, such as liquid or paste.

  It quantifies the dry matter of the composition by any conventional method within the abilities of those skilled in the art, dilutes it with distilled water as necessary, or does not significantly alter the cationic starch material it contains Concentrating by any suitable means and adjusting the dry matter in the composition to a value of 10%. Following this, the Brookfield viscosity of the resulting composition is measured at 25 ° C. in a manner known per se. For example, a rotary evaporator can be used to concentrate the composition without altering the starch material it contains.

  It should be noted that in the remainder of this application, unless explicitly stated, the amounts of cationic starch and metal salts are expressed as dry mass.

Applicants have found that when a liquid composition having a high viscosity with a cationic starch concentration of 10% of the total weight of the composition, i.e., a viscosity exceeding 1000 mPa · s, is used in a coagulation-soft flocculation process with a metal salt, It was surprisingly found that an extraordinary drop in turbidity of a solution with a solid of This is an additional use in wastewater treatment, such as described in Example 10 of WO200196403A1, which teaches the use of a liquefied composition of cationic starch in combination with cationic polyacrylamide, for example. Contrary to what is known about cationic starch mixtures with coagulants, the solution has a Brookfield viscosity according to Test A well below 1000 mPa · s. In effect, this liquid cationic starchy composition has a Brookfield viscosity of less than 1600 mPa · s when adjusted to a dry weight of 20%. Applicants viscosity of the 1600 · s were found to correspond to a Brookfield viscosity of less than 200 mPa · s according to Test A.

  According to the method of the invention, the order of steps a) and b) is not important.

  Advantageously, the time delay between steps a) and b) is less than 120 seconds, such as less than 90 seconds, and advantageously less than 60 seconds. Preferably steps a) and b) are performed simultaneously. According to an advantageous embodiment of the invention, these two steps are carried out simultaneously by adding a liquid comprising both a cationic starch and a metal salt composition, allowing a simplification of the process.

  Cationic starch can be obtained from pea starch, wheat starch, corn starch or potato starch.

  Preferably the metal salt is a sulfate, polysulfate, chloride, polychloride or polychlorosulfate. Preferably the metal salt is selected from polyaluminum chloride and ferric chloride.

  This can be added to step b), for example in the form of a solution having a concentration in the range from 0.01 to 60 g / l.

  It should be noted that when several metal salts are added in step b), the amount of metal salt is the total amount of these various metal salts.

  The process of the invention can be carried out with a total amount of cationic starch and metal salt in an aqueous solution in the range of 4 to 500 ppm. This amount is adapted to the initial turbidity of the water, which can advantageously be 5-20 ppm, preferably 5-10 ppm.

  It is particularly advantageous to carry out the process with these small amounts of coagulant. This makes it possible on the one hand to limit the processing costs and on the other hand the amount of sludge consisting of solidified suspended material that is discarded. Furthermore, by selecting these amounts of coagulant, the metal salt that remains soluble in the water recovered in step e) remains small.

  According to a first variant of the process of the invention, the cationic starch / metal salt weight ratio is 15/85 to 70/30, for example 15/85 to 60/40, preferably 15/85 to 55/45, Preferably it can reach 20/80 to 45/55.

  According to a second variant, the cationic starch / metal salt weight ratio can range from 30/70 to 60/40.

  Applicants have found that the coagulation-soft agglomeration process is particularly effective when these coagulants are charged in the above proportions.

  The cationic starch may have a degree of cation substitution in the range of 0.03 or more, preferably in the range of 0.035 to 0.2.

  The cationic starch liquid composition added in step a) preferably has a cationic starch concentration in the range of 0.01 to 50 g / L. The liquid of the composition can be any solvent of the cationic starch, preferably water.

  Agitation step c) can be carried out in the presence of an additional treatment agent, which can be selected from algae, activated carbon, and potassium permanganate. The treating agent is preferably activated carbon or potassium permanganate.

  The duration of the stirring step c) can be 1.5 minutes or more, preferably in the range of 2 to 30 minutes, more preferably in the range of 2.5 to 5 minutes.

  The separation step d) can be a tilting process. This ramping step preferably has a duration in the range of 0.25 to 1000 minutes, preferably 0.33 to 120 minutes, very preferably 0.5 to 12 minutes, for example 1 to 5 minutes.

  For further acceleration of the solidification-soft aggregation process, the floc can be ballasted using, for example, microsand.

  Thus, another advantage of the present invention is that the coagulation-soft aggregation process can be carried out in this very short time.

  In accordance with the present invention, the method can be continuous or discontinuous. In the case of a continuous process, the duration of steps c) and d) is thus the average residence time of the aqueous solution to be treated in the coagulation-soft flocculation tank and in the sedimentation separation tank, respectively.

  The method of drinking water according to the invention is particularly suitable when it comprises a purified water filtration step after the coagulation-soft flocculation step.

  The aqueous solution comprising the suspended solids to be treated may have a turbidity of 1000 NTU or less, advantageously in the range 2 to 300 NTU, preferably in the range 2.5 to 150 NTU, for example in the range 3 to 100 NTU. This aqueous solution may be surface water, such as water from a lake or stream, or groundwater.

  The method is very suitable for removing suspended particles in aqueous solutions having a size in the range of 0.001 to 500 μm, in particular in the range of 0.001 to 1 μm.

  The turbidity of the purified aqueous solution thus obtained at the end of step e) is, for example, a low turbidity of 1.5 NTU or less, preferably less than 1 NTU.

  According to the method of the present invention, the turbidity reduction can be over 98%, advantageously over 98.5%, quite preferably over 99%. The process according to the invention makes it possible to greatly reduce the turbidity, which is very advantageous in the process of drinking water.

  It should be noted that the turbidity reduction depends on the initial turbidity. When this method is used for low turbidity water, the decrease is not as great for water with higher turbidity.

  Turbidity can be measured using a WTW Turb 555IR instrument sold by the company WTW.

The liquid composition used in the present invention has a viscosity exceeding 1000 mPa · s in accordance with Test A described above. As described below, this particular viscosity is directly related to the cationic starch used and the method of preparing the composition.

  For cationic starch, the viscosity of the composition comprising it after solubilization depends on three main properties listed in order of importance: its molecular weight, its degree of branching, and its degree of cationicity. These properties are easily selected by those skilled in the art by selecting the plant source of natural starch and the preparation conditions for this cationic starch.

  The cationic starch used in the context of the present invention can be obtained from any type of natural starch of natural or hybrid origin, including starch obtained from plants that have been mutated or genetically manipulated. Said starch is in particular from potato, from high amylopectin content potato (waxy potato), from wheat, from high amylopectin content wheat (waxy wheat), from corn, from high amylopectin content corn (waxy corn), from high amylose content corn, It can be obtained from rice, from peas, from barley, or from cassava, from cuts or fractions that can be produced therefrom, and from any mixture of at least any two of the aforementioned products.

  The selection of this natural starch has an influence on the final molecular weight and its degree of branching, for example, in relation to amylose and amylopectin content.

  The cationization reaction is described in, for example, “Star Chemistry and Technology” Vol. II Chapter XVI R.I. L. WHISTLER and E.W. F. It can be performed according to one of the methods well known to those skilled in the art using cationic reagents such as those described in PASCHALL Academic Press (1967). Starch is fed to the reactor in the presence of these reagents.

  Preferably, the starch used in the cationization reaction is in granular form.

  The reaction can be carried out in the milk phase, and granular starch suspended in the solvent is cationized using temperature, time and catalysis conditions well known to those skilled in the art.

  At the end of the reaction, the starch thus cationized can be recovered by filtration, and the cationic starch can be washed and then dried.

  As an alternative, the reaction can be carried out in the dry phase, i.e. in the presence of a small amount of water added to the starch, e.g. less than 20%, preferably less than 10%, of the starch mass. Introduced into the reaction.

  Preferably the cationization reaction is carried out with a tertiary amine or quaternary ammonium salt based nitrogen containing reagent. Among these reagents, 2-diethylaminochloroethane hydrochloride such as 2-dialkylaminochloroethane hydrochloride; or those such as glycidyl-trimethylammonium halide and N- (3-chloro-2-hydroxypropyl) -trimethylammonium chloride It is preferred to use the halohydrin of which the last mentioned reagent is preferred. This reaction is carried out in an alkaline medium at a pH of more than 8 or even up to 10, the pH can be adjusted, for example, with a sodium salt.

  The reagent level used is selected such that the resulting cationic starch has the desired degree of cationic substitution (DS), where DS is the average number of OH groups that make up the anhydroglucose of the starch, substituted with cationic groups. It is.

  Those skilled in the art know how to adjust the reaction conditions to obtain a cationic starch to obtain a liquid composition useful in the present invention. In fact, the starch must not degrade to any degree during the cationization process, i.e. its molecular weight is not substantially reduced, and the compositions useful in the present invention have a suitable viscosity.

  In particular, in order to obtain a cationic starch composition useful in the present invention, it is generally necessary that the starch not undergo liquefaction treatment.

The cationic starch can be water soluble at room temperature. Soluble at room temperature means that, according to the invention, when the starch starch is charged at 10% by weight in 20 ° C. water and stirred for 1 hour, the starch solution thus obtained is 1000 mPa · s. Means having a Brookfield viscosity greater than

  According to a first variant, starch that is water soluble at room temperature is a cationic granular starch with a degree of substitution (DS) of 0.10 or higher. According to a second variant, it is pregelatinized cationic starch. This pregelatinization treatment of the cationic starch can be carried out in a drum dryer.

  In order to make a composition useful in the present invention, the cationic starch must be dissolved in a solvent. The liquid composition is generally an aqueous composition that may comprise mainly water and optionally a small amount of a water miscible organic solvent such as an alcohol such as methanol or ethanol, for example the amount of organic solvent is Less than 10% by weight of total solvent.

  To make a liquid composition useful in the present invention, the cationic starch can be made soluble in the solvent by a cooking process. This cooking in water is generally carried out by suspending cationic starch and thus forming starch milk. In order to avoid thermal degradation of the cationic starch during cooking of the milk and thus obtain an aqueous composition that meets the viscosity conditions useful in the present invention, a “mild” cooking of the starch milk is performed. Mild cooking means cooking using a temperature and / or short time that is not too high, and those skilled in the art will adapt the temperature and time to obtain a viscosity useful for making a solution. The cooking temperature is, for example, a temperature in the range of 40 to 95 ° C, preferably 60 to 90 ° C. The cooking time can range from 5 minutes to 60 minutes. The weight of cationic starch in the milk can be 10-30%, for example 20-30%.

  According to one variant, the composition is prepared using a cationic starch that is soluble at room temperature, which is preferably dissolved in water with stirring. This variant is advantageous because the starch can be easily solubilized in the liquid composition without cooking in this way. Accordingly, the compositions useful in the present invention can be readily used at the work site where the processing method is performed. In addition, since cationic starch is not cooked during preparation of the composition, starch does not pyrolyze during solubilization and is much more viscous than is obtained from the exact same starch that has undergone a cooking step in a solvent. It makes it possible to obtain a composition.

As mentioned above, the liquid composition can be used to carry out the method according to the invention. The composition comprises solubilized cationic starch and one or more metal salts selected from ferric and aluminum salts, the viscosity measured according to test A being greater than 1000 mPa · s. .

The liquid viscosity of the composition comprising cationic starch, measured according to test A, is preferably 10,000 to 100,000 mPa · s.

  Preferably, the metal salt is an aluminum salt.

  The composition advantageously has a cationic starch / metal salt weight ratio ranging from 15/85 to 70/30, preferably from 25/75 to 45/55.

  Preferably, the pH of the composition according to the invention is 3-7.

  According to an advantageous variant of the invention, a liquid composition of preservative-free cationic starch is used.

  If the cationic starch is in liquid form, degradation may be observed during its storage and product transport. In order to limit this phenomenon, it is generally necessary to add a biocide, which can be selected from phthalates, for example one of those marketed by Rohm & Haas under the trademark VINYZENE (TM). Here, the biocide concentration required for storage of starch in solution form is low, but these biocides can constitute harmful constituents in obtaining water treatment, in particular drinking water.

  The fact that starch is stored and transported in solid form limits the problem of degradation. This obviates the addition of preservatives, which can be particularly advantageous in water treatment processes.

  Thus, according to a variant of the process, a solution of preservative-free cationic starch is prepared within 24 hours before the addition step a), for example from solid form cationic starch in powder form.

The compositions useful in the present invention have a Brookfield viscosity of greater than 1000 mPa · s under the conditions of Test A. This measurement of viscosity using a viscometer manufactured by Brookfield® is well known to those skilled in the art. In particular, there are various modules for measuring this viscosity, each module suitable for a given viscosity range. All that is required is to select the appropriate module for the viscosity of the composition being measured. As an example, test A, the module of 1000 mPa · s Beyond 2000 mPa · s or less at a viscosity of less than 20000 mPa · s exceeds the module RV2,2000mPa · s of revolutions per minute 20 The viscosity revolutions per minute 20 RV5 in the viscosity exceeding module RV7,200000mPa · s of revolutions per minute 20 in viscosity of less than 200,000 mPa · s exceed 20000 mPa · s by using the module RV7 of revolutions per minute 2, it may be implemented.

  The composition comprising the cationic starch may further comprise additional components such as the metal salts or biocides described above. Thus, the dry substance of the composition useful in the present invention may consist exclusively or almost exclusively of at least one cationic starch, such as biocides or other substances such as the metal salts mentioned above. One or more other ingredients may also be included.

  The metal salt is preferably polyaluminum chloride or ferric chloride. In the case of ferric chloride, the ratio of cationic starch / metal salt is preferably 25/75 to 50/50, or even 30/70 to 40/60. In the case of polyaluminum chloride, the ratio of cationic starch / metal salt is preferably 20/80 to 45/55, or even 25/75 to 35/65.

  Although other coagulants can be used in the process, the process can be carried out without other additional coagulants, in particular without polyacrylamide and without clay.

  The coagulation-soft aggregation process can be carried out by conventional methods.

  During the first steps a) to c) of the solidification-soft flocculation process, the particles solidify in a solidification-soft flocculation tank and then form flocs.

  This tank may comprise a first tank referred to as a “coagulation tank” and a second tank referred to as a “soft flocculation tank”, the stirring speed being the second tank within the first tank. Even higher than. Advantageously, the starch composition and the metal salt are placed in a coagulation tank.

  In the case of a continuous process, the aqueous solution to be treated is fed to the tank by means of a pump, thus allowing the feed rate to be adjusted. The duration of the coagulation-soft coagulation process then depends on this feed rate and the capacity of the tank used. The salt and starch used in the present invention can be mixed with the aqueous solution to be treated before charging into the coagulation-soft flocculation tank or charged directly into the tank through a second inlet provided for this purpose. Is done. The duration of this coagulation-soft coagulation process depends directly on the tank capacity and the selected feed rate.

  The water to be treated may be pretreated to adjust its pH. Preferably, the pH of the aqueous solution comprising the suspended solids is in the range of 6 to 8.5.

  Either the gradient technique or the flotation technique can be selected to remove the floc so that the purified water can be recovered and the separation step d) can be performed. These techniques, well known to those skilled in the art, can be implemented within standard water treatment facilities.

  Preferably, sedimentation separation of the formed floc is performed in step d).

  This separation step is carried out by a gradient method, and agents such as microsand for ballasting the formed floc can also be charged into the coagulation-soft flocculation tank. These ballasted flocs are transferred with the aqueous solution to the settling separation tank so that the separation rate of the subsequent tilting process can be improved.

  The sedimentation tank can be a static sedimentation tank or a stratified sedimentation tank. The settling tank can be equipped with a scraper at the bottom for better capture of settling sludge.

  A stationary sedimentation tank is a more traditional sedimentation tank. It consists of a simple tank in which solidified particles settle to the bottom of the tank to form sludge, and purified water is recovered by a gradient method after settling.

  A stratified sedimentation tank also accelerates the sedimentation of solidified particles compared to a static sedimentation tank.

  At the end of the coagulation-soft agglomeration step, further purification steps can advantageously be performed.

  This can be, for example, a filtration step. As already explained, the coagulation-soft aggregation process used in the process according to the invention is particularly advantageous.

  This water filtration step can be an ultrafiltration or nanofiltration microfiltration step. The filter used for this is a filter comprising sand, anthracite or even activated carbon. It is also possible to use organic polymer membranes, in particular polypropylene, polyacrylamide or polysulfone membranes. To remove solutes, water filtration can also be performed by reverse osmosis using a semipermeable membrane.

  A water disinfection process may also be performed. There are a number of techniques for disinfecting liquids. It can be carried out using ozone, by ultraviolet irradiation treatment, otherwise using chlorine dioxide.

  At the end of the treatment, drinking water whose turbidity is advantageously less than 1 NTU is obtained.

  Embodiments will now be described in detail in the following examples. These illustrative examples are not intended to limit the scope of the invention in any way.

Example 1: Comparison of different coagulants for reducing turbidity of river water from the Lys River Used product:
APC: polyaluminum chloride in solution.
FeCl ₃ : Ferric chloride in solution.
PAM: Cationic polyacrylamide emulsion Flopam® DW2160.
“A”: Cationic starch solution with Brookfield viscosity of 11000 mPa · s according to Test A. This solution “A” is obtained from a cationic starch (potato base) comprising 1.2% nitrogen (expressed in dry / dry weight). This starch is water soluble at 20 ° C. Stir at room temperature for 1 hour to prepare a 1% starch solution.

protocol:
Several systems are evaluated by a jar test for drinking water from water collected from the Lys River. The water is charged with calcium carbonate (Mickart 5, average diameter 5 μm) until a turbidity of 100 NTU is obtained.

  5 grams of microsand (diameter <100 μm) is added to 1 L of water with stirring and then the coagulant (or multiple coagulants simultaneously) is added with stirring at 200 rpm for 3 minutes. The agitation is then stopped and the turbidity of the supernatant is measured 3 minutes after settling separation. The dose of coagulant used is described in milligrams of active substance per liter of water to be treated (mg / L).

  The results obtained are reported in Table 1.

  Cationic starch solution is the best coagulant at a dose of 10 mg / L. When combined with a salt such as ferric chloride or polyaluminum chloride, the turbidity is less than 1 NTU or the decrease is over 99%.

Example 2: Effect of sedimentation time on turbidity Water from the Lys river (initial turbidity: with jar test, either with Aqualenc® type polychloroaluminum sulfate solution, or with salt solution and solution A 3NTU) and the weight ratio of metal salt: cationic starch is equal to 3: 2. The total dose of salt used alone or together with salt and starch used together is fixed at 10 mg per liter of water from the Lys River. The solidification-soft aggregation process is performed in the same manner as in Example 1 except that the test was performed in the absence of sand. Turbidity was measured at different sedimentation separation times and the results obtained are reported in Table 2.

  In the absence of sand, the water treatment of the combined salt and starch reached a turbidity of less than 1 NTU with a settling separation of less than 3 minutes, whereas using salt alone takes 20-30 minutes.

Example 3 Effect of Cationicity and Starch Viscosity on Treated Water Turbidity Starch Solution Used “B”: Cationic starch solution with Brookfield viscosity of 22000 mPa · s according to Test A. This solution “B” is obtained from pregelatinized chaotic starch (potato base) comprising 0.4% nitrogen (expressed in dry / dry weight). This starch is water soluble at 20 ° C. Stir at room temperature for 1 hour to prepare a 1% starch solution.
“C”: Cationic starch solution with Brookfield viscosity of 86000 mPa · s according to Test A. This solution “C” is obtained from a cationic starch (potato base) comprising 0.3% nitrogen (expressed in dry / dry weight). The solution is prepared by cooking at 95 ° C. for 15 minutes.
“1” (comparison): a cationic starch solution with Brookfield viscosity of 2 mPa · s according to test A. This solution “1” is obtained from cationic starch (potato base) comprising 0.3% nitrogen (expressed in dry / dry weight). The solution is prepared by stirring for 1 hour at room temperature.
“2” (comparative): Cationic starch solution with Brookfield viscosity of 600 mPa · s according to test A. This solution “2” is obtained from a cationic starch (potato base) comprising 1.2% nitrogen (expressed in dry / dry weight) that has undergone a liquefaction treatment. The solution is prepared with 1% starch.
“3” (comparative): Nonionic potato starch solution with Brookfield viscosity of 200,000 mPa · s according to Test A. The solution is prepared by cooking starch in 95 ° C. water for 15 minutes.

  Various starch solutions are tested alone or in combination with a ferric chloride solution and the salt: starch weight ratio is equal to 3: 2. The total dose of starch used alone, or the salt and starch used together, is fixed at 10 mg per liter of water from the Lys River. The test protocol is the same as in Example 1 and the results obtained are reported in Table 3.

  When used alone, none of these starch solutions can reduce turbidity by more than 90%. In contrast, when mixed with a ferric chloride solution, the solutions according to the present invention (A, B, and C) can achieve a turbidity reduction of more than 99%.

Example 4: Determining Optimal Dose of Cationic Starch and Metal Salt-Based Coagulant According to the test protocol of Example 1, ferric chloride and starch solution A (salt: starch ratio 3: 2) at different doses in jars Tested together in a test.

  The results obtained are reported in Table 4.

  The mixture is therefore effective against this water from 6 mg / L and the turbidity reduction is over 99%.

Example 5: Determination of the optimal ratio of cationic starch: metal salt The various fermented chlorides from Example 1 in a jar test using various cationic starch / ferric chloride weight ratios at a total dose of 10 mg / L. Iron and starch solution A is tested. The test protocol is the same as in Example 1.

  Here, the absorbance at 254 nm of the unfiltered supernatant is also measured.

  The results are reported in Table 5. FIG. 1 also shows the gradual change in turbidity as a function of starch weight compared to the total amount of starch and metal salts.

  APC1 is aluminum polychlorosulfate in solution. This is mixed with cationic starch A. The jar test is performed at different cationic starch / aluminum salt ratios with a total dose of 10 mg / L. The test protocol is the same as in Example 1. The results are shown in Table 6.

  APC2 is polyaluminum chloride in solution. This is mixed with cationic starch A. The jar test is performed at different cationic starch / aluminum salt ratios with a total dose of 10 mg / L. The test protocol is the same as in Example 1. The results are shown in Table 7.

  APC3 is aluminum sulfate in solution. This is mixed with cationic starch A. The jar test is performed at different cationic starch / aluminum salt ratios with a total dose of 10 mg / L. The test protocol is the same as in Example 1. The results are shown in Table 8.

Example 6: Comparison of Cationic Starch Solutions of Different Plant Origin Cationic starch solutions comprising 1.2% nitrogen (expressed in dry / dry weight) are from waxy corn, amylose-enriched corn, Obtained from proteinaceous peas and from potatoes.

Used starch solution “4”: Waxy corn-based cationic starch solution with Brookfield viscosity of 1240 mPa · s according to test A.
“5”: Amylose-enriched corn-based cationic starch solution with Brookfield viscosity of 1520 mPa · s according to Test A.
“6”: proteinaceous pea-based cationic starch solution with Brookfield viscosity of 1700 mPa · s according to Test A.
“7”: Potato-based cationic starch solution with Brookfield viscosity of 1260 mPa · s according to Test A.

  According to the 3: 2 salt: starch weight ratio, various starch solutions are mixed with ferric chloride solution and tested. The coagulant mixture is used at a dose of 10 mg / L. The test protocol is the same as Example 1, and the results obtained are reported in Table 9.

Example 7: Testing on a test purification device The purpose of this example is to test the composition of the present invention in a test continuous system.

Device description:
The water to be treated is river water collected from the Lys river. It is withdrawn from the 500L tank by a pump and passed to a flow regulator. The flow meter is calibrated to 200 L / h to 600 L / h, and at its outlet is a branch tube for reagent injection. Thanks to the two small pumps connected to the flow meter, it is possible to inject two reagents at separate and different flow rates. The water and mixture then reaches the coagulation-soft flocculation tank and the tapered propeller provides the agitation required for reagent mixing. The water must then provide overflow before reaching the laminar settling tank with a 45 ° inclined sheet. Once the sedimentation tank is completely filled, the clear water overflows with the weir and flows to the sink, or it can be recovered for analysis.

  After instrument calibration, a mixture composed of Polymer A solution and ferric chloride is poured into a stirred tank at a dose of 20 mg / L starch and salt. The weight ratio of ferric chloride to cationic starch A varies as a function of the required flow rate. Table 10 shows the results of the turbidity of water at the outlet.

  These tests show the effectiveness of the method according to the invention in equipment similar to industrial equipment.

Claims (15)

a) adding a liquid composition comprising solubilized cationic starch to the aqueous solution to be treated;
b) adding one or more metal salts selected from ferric salts and aluminum salts to the treated aqueous solution;
c) stirring the aqueous solution containing these additives;
d) separating the solidified solids by sedimentation or flotation;
e) recovering purified water, comprising a coagulation-soft coagulation step, comprising:
Said steps a) and b) are carried out in any order, which can be carried out separately, simultaneously or by means of a liquid composition comprising both said solubilized cationic starch and said metal salt, Steps a) and b) are followed by said steps c), d), e),
The liquid composition comprising the cationic starch has a viscosity measured according to test A of greater than 1000 mPa · s, the test A adjusting the dry matter of the liquid composition to 10% and then the result Measuring the Brookfield viscosity of the resulting composition at 25 ° C. The method according to claim 1, characterized in that the viscosity of the liquid composition comprising the cationic starch, measured according to test A, is 1100-500000 mPa · s. The method according to claim 1, wherein the viscosity of the liquid composition comprising the cationic starch, measured according to test A, is 10,000 to 100,000 mPa · s.   4. A method according to any one of claims 1 to 3, characterized in that the time delay between steps a) and b) is less than 120 seconds.   5. A method according to any one of claims 1 to 4, characterized in that steps a) and b) are performed simultaneously. The total amount of cationic starch and metal salts in the aqueous solution, characterized in that in the range of 4～500Pp m, method according to any one of claims 1 to 5. Process according to any one of the preceding claims, characterized in that the weight ratio of cationic starch / metal salt is in the range 15/85 to 70/30.   8. A method according to any one of the preceding claims, characterized in that the separation step d) is a tilting process.   The method according to claim 1, further comprising a filtration step of the purified water after the coagulation-soft aggregation step. Step e) end the turbidity of the purified water obtained in the, characterized in that it is under 1.5NTU following method according to any one of claims 1 to 9. And solubilized cationic starch, comprises a one or more metal salts selected from ferric salts and aluminum salts, the viscosity measured according to test A exceeds 1000 mPa · s, claims 1 to 10 A liquid composition suitable for use in the method according to any one of the above. Was measured according to test A, the viscosity of the liquid composition comprising a cationic starch, characterized in that it is a 10000~100000mPa · s, the composition of claim 1 1.   The composition according to claim 11, wherein the metal salt is an aluminum salt. 14. Composition according to any one of claims 11 to 13, characterized in that the cationic starch / metal salt weight ratio is in the range of 15/85 to 70/30.   15. Composition according to any one of claims 11 to 14, characterized in that it has a pH of 3 to 7.

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